It is recognized as useful to be able to store two liquids of different density under conditions which maintain them essentially separate, even when the composition of both liquids is identical. Such separation can be achieved by two independent vessels, a single vessel with internal compartmentalization, a vessel with simple or labyrinthine fixed baffles, a vessel with a movable rigid baffle or a vessel with a flexible diaphragm or membrane. Such systems, however, have technical, operational or economic drawbacks.
A more desirable system is to maintain separation of the two different density liquids as separate layers by stratification with the lower density liquid layer above the higher density liquid layer. Even though the density of the two liquids is different, they have the same composition. This can occur because the density of the liquid used increases as its temperature decreases and the density decreases as its temperature increases. Examples of such liquids, at least over some of the most useful temperature ranges, are water, aqueous solutions of organic liquids such as methanol and ethylene glycol, aqueous solutions of inorganic salts such as sodium chloride, carbon dioxide, oil and molten salts. Such liquids are stored in stratified layers as sources of thermal energy and for refrigeration and for cooling purposes. See, for example, the U.S. Pat. Nos. 4,449,368; of Haynie 4,315,404; Schmitt et al. and 4,643,212 Rothrock.
When the lower cold layer is used for refrigeration or cooling, a stream of the cold liquid is withdrawn, used for cooling and then returned warm or hot, and at a lower density, to the top layer while cold liquid is simultaneously removed from the bottom layer. In this way, essentially the entire stored volume can be used for cooling so that the entire liquid content returned to the tank becomes heated. At an appropriate time the warm or hot liquid can be withdrawn from the tank and cooled and then returned to the tank as a lower stratified cold layer of higher density with a hot layer of lower density on top unless, of course, cooling continues until all of the hot liquid in the tank is withdrawn and returned as cold liquid.
Maintaining the described stratification of the two liquid layers having different densities requires that the liquids be withdrawn and fed to the tank without promoting undue mixing a the tank inlet and outlet and at the interface of the two liquids. The desired result can be achieved by the use of manifolds, usually including a myriad of nozzles, ports, holes, slots, perforations or other openings but they have been determined to be cumbersome and costly in fabrication, support, erection and maintenance. Accordingly, there is a need for simpler apparatus and methods for storing such stratified liquids in a tank and then simultaneously removing liquid of one density from the tank while feeding liquid of a second density to the tank.